DENVER - A neo-Nazi parolee murdered Colorado's prison chief last year after forcing a pizza delivery man whom he kidnapped and later killed to record a message denouncing the prison system, federal prosecutors said in a court filing released on Monday.

The disclosure is the first time authorities have publicly stated that ex-convict Evan Spencer Ebel killed the head of the Colorado Department of Corrections, Tom Clements, and 27-year-old pizza delivery driver Nathan Leon.

Previously, investigators stopped short of calling Ebel the trigger man in the two murders, saying only that the weapon used to kill the two men matched the handgun Ebel used when he was killed in shootout with Texas police days after the murders.

The existence of the audiotape surfaced in the case of Stevie Vigil, a Denver-area woman who pleaded guilty to buying a 9mm handgun for Ebel, an ex-convict who skipped out on his parole days before the murders in March.

Clements, 58, was gunned down at his home in Monument, Colorado, about 45 miles (72 km) south of Denver.

"Ebel rang the doorbell and shot and killed Clements when he answered the door," prosecutors said.

The murder of the high-ranking government official triggered a nationwide manhunt for the killer.

Ebel was stopped for a traffic violation near Decatur, Texas, and wounded a deputy before police shot him dead.

Colorado court records showed Ebel had been arrested at least seven times between 2003 and 2010 for such offenses as burglary, unlawful weapons possession, assault, menacing, robbery and trespassing.

Authorities said Ebel was a member of the 211 Crew, a Colorado-based white supremacist prison gang. He had tattoos of a swastika on his stomach, lightning bolts on his hands and the words "White Pride" on his arm.

Colorado prison officials released documents last year showing that Ebel spent the bulk of his sentence in solitary confinement for repeated disciplinary violations.

Ebel lured Leon to a remote location under the pretense of ordering a pizza, forced him at gunpoint into the trunk of his car, and at some point ordered him to record the statement before killing him, prosecutors said.

Leon's body was found in the Denver suburb of Golden.

In a transcript of the recording, Leon said prison authorities routinely "disrespect" inmates and their families.

"In short you treated us inhumanely, and so we simply seek to do the same, we take (comfort) in the knowledge that we leave your wives without husbands, and your children fatherless," the document said. "You wanted to play the mad scientist, well they will be your Frankenstein."

Clements was the father of two grown daughters, and Leon was the father of a 6-year-old daughter and 4-year-old twin girls.

"Leon was murdered while he tried to make extra money for his young family," prosecutors said.